Sensor

ABSTRACT

A sensor measurement device includes: an impedance analyzer to determine an impedance of a sample; a first antenna configured to generate electromagnetic radiation having a first wavelength; an impedance-matching device, positioned in a radiation path between the first antenna and the sample, to receive the electromagnetic radiation from the first antenna and transmit electromagnetic radiation of the first wavelength into the sample, the impedance-matching device comprising a metasurface including: a substrate having a thickness no greater than the first wavelength of the electromagnetic radiation; and a plurality of elements supported by the substrate, wherein: the plurality of elements are spaced apart from one another across the substrate, each element has a first dimension no greater than the first wavelength of the electromagnetic radiation, and at least two elements of the plurality of elements differ in one or more of shape or size; and a second antenna configured to receive the electromagnetic radiation from the sample.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 17/690,701, filed Mar. 9, 2022, for SENSOR, which is acontinuation of U.S. patent application Ser. No. 15/121,364, filed Aug.24, 2016, now U.S. Pat. No. 11,298,052, which is a 371 National Entry ofPCT/GB2015/05061, filed Feb. 26, 2015, which claims the benefit ofpriority to United Kingdom Application No. GB 1403389.8, filed Feb. 26,2014, each of which is incorporated herein by reference.

FIELD

The present disclosure relates to a device, structure, medium, coatingor layer arranged to couple electromagnetic radiation into or out of abiological material, improve the coupling of electromagnetic radiationinto or out of a biological sample or increase the coupling ofelectromagnetic radiation into or out of a biological sample. Inparticular, the present disclosure relates to a device, structure,medium, coating or layer arranged to reduce reflection. Moreparticularly, the present disclosure relates to an antireflectionstructure, antireflection layer and an antireflection coating. Furtherparticularly, the present disclosure relates to a metasurface.

BACKGROUND

The most common methods to analyse biological substances includeacidity, index of peroxides, UV spectroscopy, thin-layer chromatography,gas chromatography, high performance liquid chromatography, Ramanspectroscopy and UV spectroscopy. A drawback of these procedures is thatthey usually require the isolation and analysis of the componentspresent by procedures that are laborious and time-consuming. It would beadvantageous to implement new techniques that with very little or nohandling of the sample load produce results similar or superior to thoseobtained by the established procedures. Furthermore, these methods donot work well for characterizing the inner layers of a biologicalsubstance, such as the components of the blood stream which is insideanimal bodies. The skin, fat and muscle layers shield the blood fromexternal signals, making their characterization extremely difficult andprone to errors. The same problems are faced when the biologicalsubstance is inside an artificial container (bottle or opaque plasticbox), as these light-based methods do not offer penetration inside thecontainer.

A different method for characterizing substances (not just biologicalones) is dielectric spectroscopy, which utilizes microwaves or radiowaves to characterize a sample. In this approach a radio wave signal(usually generated from an antenna) is launched against the sample undertest (SUT), and the reflected and transmitted signals are recorded,leading to estimation of the electromagnetic properties of the sample(e.g., its permittivity and permeability), which can then by convertedto a material property of the sample (e.g., the percentage of sugar orsalt in water, or concentration of bacteria in milk).

Characterizing a biological substance is tremendously advantageous in aparticular sector: the concentration of glucose in the human blood (fordiabetes patients).

Diabetes is a disease characterized by high glucose levels in the blood(hyperglycaemia). It is the fifth most common cause of mortalityworldwide with a global prevalence of 8.3% and 370 million peopleaffected which is set to rise to 550 million by 2030. The cost ofdiabetes and its associated complications are staggering, estimated tobe $130 billion annually in the EU and $245 billion in the USA in 2012(up from $174 billion in 2007). The burden of uncontrolled diabetes inthe long term is substantial as it can lead to a number of secondarycomplications including; blood vessel damage, cardiovascular disease,kidney failure, neuropathy (nerve damage) and diabetic retinopathy. Asthese complications progress, they become progressively more expensiveto treat.

There is no known cure for diabetes: the condition can only be managed.Diabetes management is primarily focused on accurate measurement ofblood glucose levels using glucose meters, enabling tighter control ofblood glucose levels by injecting the correct dose of insulin (Type Ipatients) or taking oral diabetic drugs (Type II). Accurate and timelymonitoring of the blood sugar levels is therefore absolutely critical.

There are extensive costs associated with the management and monitoringof diabetes and in the EU diabetes accounts for 10% of the totalhealthcare budgets. For managing a chronic condition such as diabetes,this proves to be an extremely costly approach. Managing diabetes wellat an early stage of the diagnosis helps prevent later, more expensivecomplications. Better glucose control and management are some of theinitiatives that governments are undertaking to reduce the hospitaladmissions from uncontrolled diabetes. Therefore, there is a huge costbenefit to healthcare providers in improving monitoring adherence andaccuracy and so preventing the progressive increases in the financialburden associated with diabetes.

A non-invasive glucose monitoring system would have a substantial healthimpact. First, this would eliminate the need to draw blood from the userto take a glucose reading. This in turn eliminates the pain associatedwith lancing the finger, need for expensive strips, hygiene andinfection issues and risk of contaminating the glucose monitor resultingin potentially fatal incorrect readings. Second, it can provide accessto frequent monitoring for those that are not currently fully supportedby the healthcare systems, i.e., Type 2 diabetics and pre-diabetics.Finally, such a system is ideal for patients that rely on insulin pumpsto control their medication via a built-in feedback functionality thatautomatically adjusts the pump.

Many non-invasive biomedical applications are based on the interactionor propagation of electromagnetic radiation through biologicalsubstances, including the human body. However, fundamental challengesare identified, which arise from the very nature of the microwave fieldand its interaction with the living tissue. The skin blocks and reflectsincident radio waves, which is attributed to the high value of relativepermittivity and conductivity of the tissue compared to air. Inelectromagnetic terms, an impedance mismatch is created. This impedancemismatch results in degradation of the transmitting energy and reducedaccuracy of the applied techniques. This is probably the most criticalproblem in radio wave propagation for medical purposes. This issue leadsto different limitations in major medical applications: for example, inmicrowave imaging techniques and blood glucose monitoring, theresolution and precision is deteriorated, while in hyperthermiatreatments, higher amounts of potentially harmful energy is required.

If this impedance mismatch problem was solved, it would have tremendousimpact on the medical applications of radio waves by allowing moreaccurate devices consuming less power and occupying less space.

Recently, improvements have been made in the area and the inventors' ownearlier patent application, GB2500719, discloses a device arranged toimprove the coupling of electromagnetic radiation into a target using ametamaterial.

Metamaterials are artificially created materials that can achieveelectromagnetic properties that do not occur naturally, such as negativeindex of refraction or electromagnetic cloaking. While the theoreticalproperties of metamaterials were first described in the 1960s, in thepast 10-15 years there have been significant developments in the design,engineering and fabrication of such materials. A metamaterial typicallyconsists of a multitude of unit cells, i.e., multiple individualelements (sometimes refer to as “meta-atoms”) that each has a sizesmaller, typically much smaller, than the wavelength of operation. Itmay be said that each element has at least one “sub-wavelength”dimension. These unit cells are microscopically built from conventionalmaterials such as metals, plastics, and dielectrics. However, theirexact shape, geometry, size, orientation, and arrangement canmacroscopically affect radiation in an unconventional manner, such ascreating resonances or unusual values for the macroscopic permittivityand permeability.

Some examples of available metamaterials are negative indexmetamaterials, chiral metamaterials, plasmonic metamaterials, photonicmetamaterials, etc. Due to their sub wavelength nature, metamaterialsthat operate at microwave frequencies have a typical unit cell size of afew millimetres, while metamaterials operating at the visible part ofthe spectrum have a typical unit cell size of a few nanometres.Metamaterials can strongly absorb radiation at certain narrow range offrequencies.

For conventional materials, the electromagnetic parameters such asmagnetic permeability and electric permittivity arise from the responseof the atoms or molecules that make up the material to anelectromagnetic wave being passed through. In the case of metamaterials,these electromagnetic properties are not determined at an atomic ormolecular level. Instead, these properties are determined by theselection and configuration of a collection of smaller objects, such asconducting components or elements that make up the metamaterial.Although such a collection of objects and their structure do not “look”at an atomic level like a conventional material, a metamaterial cannonetheless be designed so that an electromagnetic wave will passthrough as if it were passing through a conventional material.Furthermore, because the properties of the metamaterial can bedetermined from the composition and structure of such small objects, theelectromagnetic properties of the metamaterial such as permittivity andpermeability can be accurately tuned on a very small scale.

GB2500719 discloses the use of a metamaterial comprising a periodicarray of unit cells. Notably, the unit cell is regular, and the array isregular. The present disclosure sets out a further improvement made bythe inventors.

SUMMARY

Aspects of the present disclosure are defined in the appendedindependent claims.

In summary, there is provided a device for coupling electromagneticradiation into or out of a biological material. The device comprises ametamaterial wherein at least two of the meta-atom elements are unlike.In particular, the size and/or shape of the metamaterial elementsdiffer. Optionally, at least some of the metamaterial elements areasymmetric or comprise only one axis of symmetry. Optionally, the arrayof metamaterial elements is irregular. The dimensions of the componentelements are optimised for the application. There is also provided asensor comprising two coupling devices.

The elements of the metamaterial are arranged to affect the amplitudeand/or phase of the electromagnetic radiation. The elements of themetamaterial in accordance with this disclosure are not designed toprovide significant energy storage. By tuning the size, shape,dimensions and positioning of the component elements, reflectivity maybe reduced. The reflectivity may be caused by a containing componentsuch as skin or a bottle. Other effects may be imparted on theelectromagnetic radiation such as wave focusing.

According to one aspect, a sensor measurement device is provided. Thesensor management device includes an impedance analyzer to determine animpedance of a sample. The sensor measurement device also includes afirst antenna configured to generate electromagnetic radiation having afirst wavelength. In addition, the sensor measurement device includes animpedance-matching device, positioned in a radiation path between thefirst antenna and the sample, to receive the electromagnetic radiationfrom the first antenna and transmit electromagnetic radiation of thefirst wavelength into the sample. The impedance-matching devicecomprises a metasurface including a substrate having a thickness nogreater than the first wavelength of the electromagnetic radiation and aplurality of elements supported by the substrate, where the plurality ofelements are spaced apart from one another across the substrate, eachelement has a first dimension no greater than the first wavelength ofthe electromagnetic radiation, and at least two elements of theplurality of elements differ in one or more of shape or size. The sensormeasurement device further includes a second antenna configured toreceive the electromagnetic radiation from the sample, wherein one orboth of the first antenna and the impedance-matching device are tunablebased on the impedance of the sample to reduce an impedance mismatchalong the radiation path.

In an example, sample comprises a biological sample.

In another example, metasurface is configured to impose a specific phaseand amplitude change along an incident wave of the electromagneticradiation.

In yet another example, the impedance-matching device, the firstdimension is the direction for propagation of the electromagneticradiation.

In still another example, at least one of the plurality of elements ofthe metasurface has an irregular shape.

In an example, the sample is bound by a container, and theimpedance-matching device is configured to transmit the electromagneticradiation of the first wavelength into the sample from a positionoutside the container.

In another example, at least a subset of the plurality of elements ofthe metasurface are arranged in an irregular array. Alternatively, theplurality of elements of the metasurface are arranged in an irregulararray.

In yet another example, the substrate is a dielectric, and the pluralityof elements are conductive. Alternatively, the substrate is conductive,and the plurality of elements are a dielectric.

In still another example, the plurality of elements are collectivelyarranged to resonate at the first wavelength of the electromagneticradiation.

In an example, the impedance-matching device further comprises anadditional metasurface coupled to the metasurface, where the additionalmetasurface comprises a substrate comprising a thickness no greater thana second wavelength of the electromagnetic radiation and a plurality ofelements supported by the substrate, wherein each element has a firstdimension no greater than a second wavelength of the electromagneticradiation, at least two elements of the plurality of elements arenon-identical, the additional metasurface is arranged, in cooperationwith the metasurface, to resonate at a second wavelength of theelectromagnetic radiation, and the first wavelength is different fromthe second wavelength.

In another example, the additional metasurface shapes at least one of anamplitude or phase of the electromagnetic radiation.

In yet another example, the sensor measurement device further comprisingan electronic calliper arranged to determine a distance between thefirst antenna and the second antenna.

In still another example, one or both of the first antenna and theimpedance-matching device comprise a tunable component including one ormore of a varactor or a variable resister.

In an example, the sample comprises blood, the sensor measurement deviceis arranged to measure a blood glucose level, and the sensor measurementdevice is wearable on at least one of a hand, a foot, an ear, or a lip.

In another example, the first antenna, the impedance-matching device,and the second antenna are physically associated.

In yet another example, the sensor measurement device further includes asecond impedance-matching device arranged between the sample and thesecond antenna to transmit electromagnetic radiation of the firstwavelength from the sample to the second antenna, the secondimpedance-matching device comprising a metasurface including a substratehaving a thickness no greater than the first wavelength and a pluralityof elements supported by the substrate, where the plurality of elementsare spaced apart from one another across the substrate, each element hasa first dimension no greater than the first wavelength, and at least twoelements of the plurality of elements differ in one or more of shape orsize.

According to another aspect a method is provide for couplingelectromagnetic radiation into a sample using a sensor measurementdevice. The method includes positioning the sensor measurement devicewith respect to the sample such that the first antenna is disposed on afirst side of the sample and the second antenna is disposed on a secondside of the sample. The method also includes determine an impedance of asample. The method further includes tuning one or both of the firstantenna or the impedance-matching device based on the determinedimpedance to reduce an impedance mismatch along the radiation path. Inaddition, the method includes providing electromagnetic radiation havingthe first wavelength from the first antenna to the impedance-matchingdevice. The method also includes transmitting, by the impedance-matchingdevice, electromagnetic radiation having the first wavelength from thefirst antenna into the sample. The method further includes receiving, bythe second antenna, electromagnetic radiation from the sample. Themethod additionally includes characterizing the sample based on thereceived electromagnetic radiation.

According to another aspect, a method for designing animpedance-matching device for a sensor measurement device is provided.The method includes positioning the first antenna on a first side of thetest sample and the second antenna on a second side of the test sample.The method also includes determining an impedance of the test sample.The method further includes calculating a sheet impedance for themetasurface that will couple the electromagnetic radiation of the firstwavelength into the sample with maximum transmission. In addition, themethod includes using analytical modelling to design the plurality ofelements of the metasurface such that, when the plurality of elementsare combined together in a pattern, cause the metasurface to have thecalculated sheet impedance.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described withreference to the accompanying drawings in which:

FIG. 1 is a metasurface having a periodic pattern;

FIG. 2 is a metasurface having a non-periodic pattern;

FIG. 3 shows multiple metasurface layers in a periodic configuration;

FIG. 4 shows multiple metasurface layers in a non-periodicconfiguration;

FIG. 5 shows real and imaginary sheet impedances to refract a normallyincident electromagnetic wave to an angle of 45 degrees;

FIG. 6 shows reflection and transmission coefficients derived from thesheet impedances of FIG. 5 ;

FIG. 7 illustrates various views of the metasurface element of thedesign example;

FIG. 8 plots S-parameters obtained changing the length of the parallelcopper bars of the top metasurface component of the design example;

FIG. 9 plots S-parameters obtained changing the gap of the metal ring ofthe bottom metasurface element;

FIG. 10 shows optimisation progress for the metamaterial elementdimensions;

FIG. 11 a shows the optimised geometry characteristics for themetasurface element at 60 GHz;

FIG. 11 b is a metasurface structure in accordance with embodiments;

FIG. 11 c, 11 d and 11 e are further views of a metasurface structure inaccordance with embodiments;

FIGS. 11 f, 11 g and 11 h show an example of a planar near-fieldfocusing component;

FIG. 11 i shows a simulation result of the power penetration in the casewhen the metasurface in accordance with the present disclosure is placedagainst human skin;

FIGS. 12 a to 12 m show some design configurations;

FIG. 13 is an overview of the system;

FIG. 14 a shows system components of the sensor measurement device inaccordance with embodiments;

FIG. 14 b shows system components of another sensor measurement devicein accordance with embodiments;

FIGS. 15 a to 15 d show some examples of single and dual sensors;

FIG. 16 shows a tuning antenna with an impedance analyser;

FIGS. 17 a to 17 c show the sensor in use;

FIGS. 18 a and 18 b are isometric views of a measurement system througha human hand;

FIGS. 19 a and 19 b are exploded views of a metasurface with antennaconfiguration in (a) period and (b) non-periodic patterns;

FIG. 20 is an exploded side view of antenna and three metasurfacelayers;

FIG. 21 plots an output signal as a function of glucose concentration ina sample containing water and glucose;

FIG. 22 plots an Output signal as a function of concentration in samplescontaining water and glucose, water & glucose & salt, and water & salt;

FIG. 23 plots an output signal as a function of glucose concentration insamples containing water and glucose in very small amounts;

FIG. 24 shows an output signal as a function of the concentration ofpalm kernel oil in a mixture of palm kernel and rapeseed oil; and

FIG. 25 shows relaxation frequencies of the Cole-Cole model fordifferent oil species.

In the figures, like reference numerals refer to like parts.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments refer to “biological material” which is a material that istypically either plant material, animal material, or some othersubstance that can be found in a life form. Some examples include humantissue (hand, skin, muscle, ear, etc.), animal tissue (e.g. from amouse, cow, or pig), water, blood, milk, saliva, tears, urine,carbonated drinks, and fruit juice, wine, and oil. However, it may beunderstood that the present disclosure is equally applicable to anybiological sample.

Embodiments refer to “irregular” shapes which include shapes having noaxis of symmetry and shapes having only one axis of symmetry.

A metamaterial comprises a substrate component having a thickness nogreater than a first wavelength of the electromagnetic radiation; and aplurality of elements supported by the substrate component, wherein eachelement has a first dimension no greater than a first wavelength of theelectromagnetic radiation. Embodiments refer to a “metasurface” whichmay be considered a special type of metamaterial. Specifically, ametasurface is a metamaterial in which at least two of the elements ofthe plurality of elements are non-identical, or different, in any one ormore of size, shape, orientation and composition. A metasurface is onlytwo-dimensional.

Device for Coupling Electromagnetic Radiation

In overview, the present disclosure describes use of certain types ofmetamaterials to enhance radio wave penetration through the skin and,therefore, solve the mismatch problem. This is achieved by harnessingthe novel and special electromagnetic properties of a subset ofmetamaterials.

Conventionally, metamaterials comprise unit cells arranged in periodicpatterns. However, the inventors have recognised that a specific type ofmetamaterial, sometimes called a “metasurface”, is particularlyadvantageous for coupling electromagnetic radiation into biologicalsamples particularly biological samples in a container.

Metasurfaces are easy to fabricate and offer the opportunity to buildlow-loss structures. The properties of the metasurface are determinedfrom the periodicity and the design of their constituent elements. Notethat, unlike other metamaterials, which are periodic arrangements of thesame element, a metasurface usually comprises of different elements.Likewise, the elements of a metasurface are not necessarily periodicallyarranged. The present disclosure relates to a metamaterial in which atleast two of the sub-wavelength elements of the plurality of elementsare different in shape and/or size and/or composition and/ororientation.

FIG. 1 shows a metasurface 100, in accordance with the presentdisclosure, comprising a substrate component 101 and a plurality ofelements 103. As shown in FIG. 1 , elements 103 differ in size andshape. However, in this embodiment, elements 103 are arranged in asubstantially regular array. That is, the spacing between the centres ofadjacent elements is substantially constant in two orthogonaldirections.

There is therefore provided a device arranged to couple electromagneticradiation, the device comprising a first metamaterial comprising: asubstrate component having a thickness no greater than a firstwavelength of the electromagnetic radiation; and a plurality of elementssupported by the substrate component, wherein each element has a firstdimension no greater than a first wavelength of the electromagneticradiation and at least two of the elements of the plurality of elementsare non-identical.

Advantageously, the inventors have found that using a metasurfacesignificantly reduces the losses associated with resonances occurring inconventional metamaterials. In fact, it is found that a nearly loss-lesssystem can be produced using a metamaterial wherein at least two of theelements of the plurality of elements are non-identical. Furtheradvantageously, this type of metamaterial is very thin and easy tofabricate. This makes it even more preferable as a sensor for biologicalmaterials particularly biological materials in a container. Inparticular, it makes the device particularly suitable as anantireflective component such as an antireflection coating. Theseadvantageous are achieved because impedance matching and/or shaping ofthe electromagnetic radiation can be achieved when differing size and/orshape elements are used.

In an embodiment, the first dimension is the direction for propagationof the electromagnetic radiation. In embodiments, the first dimension isthe thickness of each element. Accordingly, the elements are notdesigned to provide substantial energy storage which requires greatervolume. In embodiments, all dimensions of each element are less than thewavelength of the electromagnetic radiation. In embodiments, the firstwavelength comprises a bandwidth of wavelengths including the firstwavelength.

Some of the elements 103 shown in FIG. 1 may be considered irregularand/or asymmetric. That is, in an embodiment, at least one of theelements of the plurality of elements has an irregular shape. In anembodiment, all the elements of the plurality of elements have anirregular shape. Advantageously, this allows for finer tuning of thecharacteristics of metasurface because more degrees of freedom areavailable in the tuning of its performance.

In an embodiment, the biological material is bound by a container. Inembodiments, the biological material is enclosed by the container. In anembodiment wherein the biological material is blood, the containerincludes skin. In an embodiment wherein the biological material is foodstuff, the container is a plastic bottle. Further examples are givenbelow.

FIG. 2 shows an embodiment in which the elements are arranged in anon-periodic pattern. FIG. 2 shows a metasurface 200 comprises asubstrate component 201 and a plurality of irregularly positionedelements 203. The elements 203 are also irregular in size and shape. Itis not essential that all elements in the array of elements areirregularly arranged. In an embodiment, at least a subset of theelements is arranged in an irregular array. In a further embodiment, allthe elements are arranged in an irregular array. Advantageously,irregularity in the positioning of the elements allows for finer tuningof the characteristics of metasurface.

The metasurfaces shown in FIGS. 2 and 3 are substantially planar. Thatis, in an embodiment, the substrate component is planar. The metasurfaceis designed for electromagnetic radiation to pass through in a directionperpendicular to the plane of the metasurface. In other embodiments, themetasurface is non-planar or curved such as spherical or cylindrical. Inembodiments, the substrate is flexible. Losses associated withtransmission through the metasurface are reduced because theelectromagnetic radiation passes through a smaller volume ofmetamaterial.

In an embodiment, the substrate component is a dielectric, and theelements are conducting. In an embodiment, the elements are formed fromany conducting material including homogeneous materials such as metalsas well as composites and nanocomposites including Bragg reflectors. Theelements may be formed, for example, from silver, gold, copper and/oraluminium, or any other metal that supports reflections at thewavelength of interest.

The skilled person will understand that any suitable technique forproducing the conducting component on a dielectric support structure maybe appropriate. In embodiments, etching, photoresist etching, e-printingor lithographic techniques are used. In other embodiments, aself-assembly chemical process is used.

In an alternative embodiment, the substrate component is conducting, andthe elements are a dielectric.

The thickness of the elements may be few micrometres to a fewcentimetres. At least one dimension of the elements is sub-wavelength.

The “sub-wavelength” periodic arrangement of metallic and dielectricelements allows the periodic conducing component to resonate at aresonant frequency (or wavelength). The skilled person will understandthat there may be a narrow band of frequencies centred on the resonantfrequency at which at least partial resonance will occur. At theresonant frequency, radiation will be at least partially “captured” bythe metamaterial and amplification may occur by constructiveinterference, for example. The metamaterial forms a type of waveguide inwhich the fields inside the “waveguide” are bound and contained,permitting amplification. Accordingly, there is provided a devicearranged to increase the penetration of radiation into a target.

In embodiments, the device is tuned to the source and target medium. Itis found that an incident wave travels along the path of leastresistance of the conducting component of the metamaterial. For example,if source provides a plane wave of radiation, symmetric conductingelements may be preferred. The shape and configuration of the conductingmay also be chosen to match the polarisation of the incident radiation.For example, conducting elements having horizontal and vertical featuresmay be preferred for horizontally and vertically polarised radiation.

The conducting elements may comprise features having a length optimisedfor a wavelength of interest. In embodiments, the length of a primaryfeature is approximately half the wavelength of the incident radiation.For example, a conducting component having a long element, such as aspiral or a regular meander, will have a relatively long resonantwavelength. For example, the number of turns in the spiral of regularmeander may be increased to increase the resonant wavelength. Theconducting elements may comprise a sense of rotation such as aleft-handed or right-handed spiral optimised for circularly orelliptically polarised radiation, for example. The shape and dimensionof the elements may be optimised experimentally or numerically.

In embodiments, optimization of the shape of the elements is achievedvia numerical simulation such that the device enhances the penetrationof waves at a particular wavelength. The shape of the elements can alsobe optimised to modify the amplitude and phase of the incident wave in away that the output wave has particular properties, such as maximizedtransmission, or a phase front result in a focusing wave, or a wave witha specific polarisation (e.g. linear or right-hand circular). In oneembodiment, there is designed a model of the system in anelectromagnetic simulator. The model includes all the components of thesystem: the source medium, the device component or components, thetarget medium, and any other features embedded in the target medium thatneeds to be imaged. Then the electromagnetic properties as a function offrequency of each component are specified, such as the electricpermittivity, permeability, conductivity, or loss. Then the S-parameters(reflection and transmission) of the system are evaluated as a functionof frequency. The frequency range where the transmission is maximizedmay indicate the optimal operational range of the system. In otherembodiments, the aim is not to maximise transmission but to form atransmitted wave having a particular phase and amplitude at eachlocation behind each metasurface element. For example, the phase may bechanged linearly along the metasurface elements to form an output wavewhich propagates at an angle compared to the incident one. When thegeometry of the elements is modified, the transmission peak will bevaried accordingly. Thus, one can modify the shapes (or their period) totune the operational frequency to the frequency or frequencies ofinterest (e.g., the radiation frequencies of the antenna system thatgenerates the incident waves).

An operational principle of the metamaterial is that it is highlyresonant around specific frequencies. For those frequencies, the wavetransmission through the array is enhanced multiple times and thusincreased wave penetration through the target occurs. That is, theplurality of elements are collectively arranged to resonate at a firstwavelength of the electromagnetic radiation. The resonance condition isdetermined by the geometry of the array elements and is optimized fortransmission when it is placed on top of a particular target. That is,the components of the device are tailored to the target.

Each element of the plurality of elements may be individually tuned tothe source, container. and biological material. To design a metasurfacein accordance with the present disclosure, it may be modelled as atransmission line element. For example, the metasurface can act as amatching stub between the two media, and its impedance can be designedsuch that the desired transmission from one medium to another isoptimized. The transmission coefficients are related to the sheetimpedances using analytical modelling. Then, the impedance of themetasurface will determine the custom design of the unit element (e.g.,tested with simulation software), which, when combined in a pattern willcreate the metasurface with the necessary response at the frequency ofinterest to allow the high transmission of incident radiation with minorreflections.

In embodiments, metasurfaces are designed and used specifically tointeract with human tissue on the transmitted side. The metasurface isspecifically designed to 1) maximize the transmission through the tissueor biological sample, and/or 2) focus the incident energy on aparticular spot inside the receiving sample. This can be achieved byoptimizing the shape of the metasurface elements based on the desiredphase that should be imparted on the incident wave.

The transmission line theory implies that the metasurface can act as amatching stub between the air and the skin tissue. By knowing thecharacteristics of air and skin, the transmission and reflectioncoefficients can be derived and related to the sheet impedance of themetasurface. These impedance characteristics will determine the customdesign of the subwavelength unit element, which microscopically will“manipulate” the incident wave and provide the necessary reactance forthe impedance matching. This custom design is obtained performing somenumerical calculations using a numerical computing environment. Afterthis modelling, the calculated structures are evaluated and optimizedusing electromagnetic evaluation software.

The substrate serves as a support structure for the shaped elements. Inembodiments, the shaped elements are coated on the surface of thesubstrate. In other embodiments, the shaped elements are embedded withinthe substrate. The skilled person will understand that the array ofshaped elements may be supported on the substrate in a variety of ways.In embodiments, the substrate is flexible. In embodiments, the device isa multilayer device comprising a plurality metallic-comprising layersand/or dielectric-comprising layers.

Metasurface Design Example

The following is an example of how to design a metasurface array.

The purpose of the metasurface is to impose a specific phase andamplitude change along an incident wave. The properties of themetasurface are extracted by the ratio of the desired electric andmagnetic field before and after the metasurface.

The first step to design the metasurface is to determine the necessarysheet impedances at the operating frequency.

$\begin{matrix}{Y_{es} = {\frac{2\left( {H_{1}^{z} - H_{2}^{z}} \right)}{E_{1}^{y} - E_{2}^{y}} = \frac{2 - {2^{5/4}e^{- {{jkysin}(\phi)}}}}{\eta + {2^{1/4}e^{- {{jkysin}(\phi)}}}}}} & (1.1)\end{matrix}$ $\begin{matrix}{Z_{ms} = {\frac{2\left( {E_{1}^{y} - E_{2}^{y}} \right)}{H_{1}^{z} - H_{2}^{z}} = \frac{{2\eta} - {2^{5/4}\eta{\cos(\phi)}e^{- {{jkysin}(\phi)}}}}{1 + {2^{1/4}e^{- {{jkysin}(\phi)}}}}}} & (1.2)\end{matrix}$

Here Y_(es) and Z_(ms) are the sheet admittances and impedances of themetasurface (which are a function of frequency and position). H and Eare the electric and magnetic fields around the metasurface: thesuperscripts (y or z) indicate the vector field components, while thesubscripts indicate the position before (index=1) or after (index=2) themetasurface. In this example the wave propagates along the x-direction,and the metasurface is located in the y-z plane.

This example relates to the design of a metasurface to refract anincident plane wave originating from air into a 45-degree angle at a 60GHz frequency. It can alternatively be designed to focus the wave at aparticular spot inside the target medium (e.g. biological material) onthe transmission side, or exactly match the impedance (maximizetransmission). The important factor is the ratio of the desired electricand magnetic fields exactly before and immediately after the metasurfaceelements.

The results obtained after calculating the fields along the metasurfacelength (perpendicular to the direction of propagation) are shown in FIG.5 .

In FIG. 5 , periodicity is shown. This periodicity will lead to aperiodic metasurface, which will be subdivided in individual unit cells.A typical number is between 5-20 elements for each period along the yaxis, although more (smaller) elements can be used to increase theresolution.

Once the sheet impedances are known, it is possible to extract thevalues of the reflection and transmission coefficients using equations1.3 and 1.4.

$\begin{matrix}{T = \frac{\eta\left( {4 - {Y_{es}Z_{ms}}} \right)}{\left( {2 + {\eta Y_{es}}} \right)\left( {{2\eta} + Z_{ms}} \right)}} & (1.3)\end{matrix}$ $\begin{matrix}{R = {\frac{2}{2 + {\eta Y_{es}}} - \frac{2}{{2\eta} + Z_{ms}}}} & (1.4)\end{matrix}$

Here η is the wave impedance of the background medium. FIG. 6 shows thereflection and transmission coefficients derived from the sheetimpedances of FIG. 5 .

The metasurface in accordance with the present disclosure is made ofdifferent unit cells, the study will focus on designing one of them. Inan embodiment, to start the design, one of the unit cells isdeliberately “tuned out”. In this example each metasurface elementconsists of two sub-elements on either side of a dielectric substrate(e.g. Teflon).

FIG. 7 shows various views of a metasurface element in accordance withthis example.

The goal is to obtain S-parameters in accordance with equation 1.5 inorder to achieve the correct performance for this block.

S ₁₁=−0.1327+0.1107i S ₂₁=−0.3290−0.9360i  (1.5)

FIG. 8 shows the obtained simulated S-parameters of the metasurfaceelement as the length of the rods in the top element and the gap in thering in the bottom element is varied.

FIG. 9 shows the S-parameters obtained changing the gap of the metalring of the bottom metasurface element.

From this, it is possible to make a first approximation to the solution.However, to obtain the most accurate values, it is necessary to do anoptimization. This optimization may be performed, for example, insimulation software.

FIG. 10 shows optimisation progress for the metasurface elementsdimensions.

After optimization, the resulting S-parameters are:

S ₁₁=−0.1327+0.03968i S ₂₁=−0.3245−0.9261i  (1.6)

The optimized metasurface element is shown in FIG. 11 a . The optimisedS-parameters are indicated with vertical lines in FIGS. 8 and 9 . Inembodiments, each metasurface element is generally or substantiallycross-shaped.

Each metasurface element can be designed in a similar fashion.

In an embodiment, there is provided a metasurface which comprises acombination of metallic crosses and so-called Jerusalem crossesseparated by a dielectric substrate. In embodiments, the dielectricsubstrate is a liquid crystal polymer. FIG. 11 b shows an exploded viewof an embodiment comprising two metallic patterned layers separated by adielectric and sandwiched between two dielectric layers (5 layerstotal). FIG. 11 c is a schematic of the bare metasurface structure (twometallic patterns on either side of a dielectric). In embodiments, themetallic parts are embedded into the dielectric. In other embodiments,the metallic parts protrude the dielectric. FIGS. 11 d and 11 e show topand bottom views of the metallic layers.

In embodiments, the metasurface elements are optimised to induceconvergence of the near-field. These “near-field focusing structures”can lead to focusing details of size well below the diffraction limit.Accordingly, the metasurface may be designed to provide focusing insidea sample—for example, a biological sample in a container. Inconventional materials, focusing is usually achieved by properly shapinga homogenous material (e.g. glass), producing lens-type structures. Withmetasurfaces in accordance with the present disclosure, the shape of thestructure can remain flat, but it is no longer homogenous, as itconsists of different metallic and dielectric elements.

Additional Layers

The device may comprise a plurality of metasurfaces wherein eachmetasurface is tuned differently. For example, each metasurface may bearranged to resonate at a different wavelength. In embodiments, by atleast partially overlapping the resonant wavelengths of a plurality ofmetasurfaces, a pseudo-broadband device is formed. For apseudo-broadband device, the resonant frequency of adjacent layers maydiffer by an integer multiple of a half wavelength, for example.

In an embodiment, the device further comprising a second metamaterialcoupled to the first metamaterial, wherein the second metamaterialcomprises: a substrate component having a thickness no greater than asecond wavelength of the electromagnetic radiation; and a plurality ofelements supported by the substrate component, wherein each element hasa first dimension no greater than a second wavelength of theelectromagnetic radiation and at least two of the elements of theplurality of elements are non-identical.

In an embodiment, the second metamaterial is arranged, in cooperationwith the first metamaterial, to resonate at a second wavelength of theelectromagnetic radiation.

In an embodiment, the first wavelength is different to the secondwavelength. In embodiments, the second wavelength also comprises abandwidth of wavelengths including the second wavelength.

In embodiments, there is provided an additional near-field focusingcomponent which is dedicated to providing the near-field focusingdescribed above. In embodiments, the near-field focusing component isplaced immediately adjacent the device for coupling EM radiation inaccordance with the present disclosure. In an embodiment, the near-fieldfocusing component is a 22 mm by 22 mm by 0.368 mm structure, made up ofsmaller square unit cells with a period of 2 mm. The unit cell comprisesthree layers of metallic elements separated by dielectric layers. Unitcells with a large range of transmission (S21) phases are required forthe lens. Numerical simulation may be used to find suitable designs byvarying parameters to affect the S21 phase and magnitude. The inventorsfound that single elements did not provide larger phase ranges and so,in embodiments, the near-field focusing component comprises multiplelayers of elements. In embodiments using a three-layer design, theinventors found that it was possible to keep the total transmissionhigh: all unit cells chosen had a S21 magnitude greater than 0.8. Unitcells with three layers of elements, produced a 360° S21 phase range. Inembodiments, the outer two elements are rectangular bars, and the innerelements are split ring commutators. The target focal length was 18 mm.

An example near-field focusing component is shown in FIG. 11 f(perspective view), 11 g (front view) and 11 h (back view).

In embodiments, there is provided an additional layer between theantenna and the device for coupling EM radiation which shapes theelectromagnetic waves emitted by the antenna. This additional layer maybe considered a beam-shaping layer. The beam-shaping layer shapes theamplitude and/or phase of the radiation pattern. In embodiments, thebeam-shaping layer optimises the shape of the radiation pattern for thedevice for coupling EM radiation in accordance with the presentdisclosure. In embodiments, this layer is an appropriately shapeddielectric or non-metallic material. In other embodiments, this layer isitself a metamaterial or metasurface such as a periodic combination ofmetal parts on a dielectric substrate. In embodiments, the beam-shapinglayer comprises Teflon, liquid crystal polymer, Rogers 3000 or Rogers400 series materials, or other dielectric materials that adds phase tothe impinging waves. In embodiments, the beam shaping layer alsocomprises copper, alumina, or other highly conductive material.

In embodiments, there is provided a disposable biocompatible layerarranged to couple the device to a target. In embodiments, thedisposable biocompatible layer may be provided for reasons of hygiene.In other embodiments, the disposable biocompatible layer may comprise adielectric component, optionally, supporting a planar array ofconducting elements. The disposable biocompatible layer may therefore be“tuned” to the rest of the device. The disposable biocompatible layermay be deformable and/or may have a morphology arranged to attach to apart of the human body. The disposable biocompatible layer may be formedfrom a polymer-based material.

It may therefore be understood that, in embodiments, the device is amultilayer device comprising a plurality of metallic-comprising and/ordielectric-comprising layers. Advantageously, a multilayer structure maybe arranged to cover a suitably large phase range whilst maintaininghigh transmission. In embodiments, the structure comprises at leastthree metasurface layers. In embodiments, each layer has a thickness of□/200 to □/3, optionally, □/150 to □/50, further optionally, □/120 to□/80. Advantageously, the inventors have found that this restriction onthe thickness of each layer ensures that waves of interest are notoverly attenuated due to propagation (expanding beams) before reachingthe target (or fully transmitting through the device). This restrictionon the thickness of each layer also helps minimise the device size.

Sensor for Biological Material

In an embodiment, there is provided a wearable device that clips ontothe earlobe, hand, or other body part rich in blood and non-invasivelymonitors changes to blood glucose levels in real time, eitherinstantaneously or continuously. The radio wave sensors transmit andreceive thousands of individual low power radio wave signals tissue thatare then combined to obtain accurate blood glucose readings usingalgorithms. Optionally, the glucose readings are displayed withinseconds on the device, or they can be transmitted via Bluetooth to amobile app, where the patient can manage the data and receive alerts.Further optionally, the data are then securely uploaded to an encryptedcloud-based historical record system, available to the patient or adoctor.

In an embodiment, there is provided non-invasive glucose measurementsvia the transmission and reflection of non-ionizing millimetreelectromagnetic waves through the human blood. The devices in accordancewith the present disclosure are applicable in the range 10 to 300 GHz.However, in an embodiment, the frequency of the waves is around the40-100 GHz band, which is an available part of the spectrum open tomedical and communication applications. Historically, this frequencyband has not been adequately explored for glucose measurements.

There are two main methodologies for non-invasive glucose monitoringusing electromagnetic waves. The first utilizes low-frequency radiowaves, typically in the MHz or a few (up to 5) GHz region. The secondutilizes much higher frequencies at the optical part of the spectrum.The fundamental limitation of both methods has always been the problemof bypassing the skin layer, causing sampling only at the interstitialfluid layer thus limiting their effective accuracy and speed. It hasbeen reported that at the interstitial fluid layer glucose sensitivityis delayed by up to 30 minutes compared to intra-venous sampling. Theinterstitial fluid lies right beneath the skin and outside the bloodarteries and capillaries.

Measurements in this band offer two distinct advantages that aresuperior to other non-invasive methods. First, the wavelength of thewaves (around 5 mm in air) is large enough to allow penetration throughhuman tissue such as the earlobe, yet simultaneously small enough toprovide enough resolution of the blood regions inside it. Second, thesmall wavelength requires an equally small antenna to generate them.Thus, a mobile miniaturized wireless sensor that can be continuouslyworn on the human body, e.g. ear, is feasible, incorporating all thenecessary electronics and processing power to perform the glucosemeasurements.

Compared to optical methods, where the wavelength is much smaller (inthe few micron range) the 40-100 GHz band is further advantageousbecause it generates waves with wavelength that are long enough topenetrate well into a biological sample. Water-based samples and tissuesamples typically have very high loss and produce significant impedancemismatch, and thus a wave with shorter wavelength will perceive anelectrically longer structure to penetrate through, attenuatingsignificantly along the way. The inventors have identified 1000 GHz asthe maximum frequency beyond which the wavelength is too short topenetrate deep enough through a biological sample without attenuatingtoo much.

Compared to other methods of dielectric spectroscopy that utilizemicrowaves or radio waves, they typically operate at much lowerfrequencies (longer wavelengths), up to 10 GHz where the wavelength is 3cm. These waves are long enough to perceive an electrically small samplewithout much attenuation. However, with some samples, they may not smallenough to resolve details inside a sample, providing only averagedmacroscopic information. In addition, if the sample is thin, e.g. 3 mmor less (such is the case for the earlobe), then a wave that is at least10 times longer will be unable to sense any high-accuracy informationfrom that sample. Thus, in an embodiment, 40 GHz is the lowest frequencybelow which the wavelength is too long to sense small details andingredients in a sample with high, reproducible accuracy.

As a result, the inventors have found that 10-300 GHz, optionally 40-100GHz, is the optimum band to produce accurate sensing measurementswithout attenuating the waves. More specifically, the inventors havefound that two bandwidths, 59-64 and 68-72 GHz, are particularlysuitable for a range of biological samples. In embodiments, theinventors have found that better results are achieved when the bandwidthis 4-6 GHz.

Many attempts have been made in the past to estimate glucose levelsusing resonating methods. These methods are extremely accurate, and theyare commonly used for many years in characterizing materials. There isno question that they could be used to measure glucose accurately if allother factors remained constant. However their greatest strength is alsotheir greatest weakness: if you try it on a different person, or for anyphysiological skin changes (e.g. aging, during pregnancies, sweating/wetor dry skin etc.), then the measurement will provide spurious readings.The skin has pores which our body uses to maintain a constanttemperature. Something as simple as moving to a hotter room will triggerthe production of sweat in the glands which will throw the measurementaccuracy off. The structure in accordance with the present disclosuremitigates the effects of the skin and/or allows electromagneticradiation to substantially penetrate the skin where it would otherwisebe reflected.

In embodiments, the device in accordance with the present disclosure isarranged to minimise the reflection off skin and other certainbiological tissue. In embodiments, the biological material of interestis blood, and the device is arranged to minimise the reflection offskin. In embodiments, there is therefore provided an antireflectioncoating for skin. In these embodiments, the skin may be considered acontainer for the biological material of interest.

FIG. 11 i shows a simulation result of the power penetration using ametasurface, in accordance with the present disclosure, against humanskin. Specifically, FIG. 11 i shows the power reflected in, powertransmitted, and power dissipated against frequency for the structure incontact with a layer of skin 0.58 mm thick. Solid lines correspond tothe setup consisting of the metasurface and the skin and dashed linescorrespond to a setup consisting of the skin only without metasurface.

The total thickness of the metasurface structure is 150 □m. The additionof the metasurface produces a decrease from 39% to 0.16% in thereflected power and an increase from 56% to 94% in the dissipated powerat 60 GHz. The transmitted power increases from 4.5% to 6.3%. The mainreason that a perfect transmission is not achieved is the presence ofloss in the structure.

Sensor Configurations

Schematic representations of the sensor are shown in FIGS. 12 a to 12 m. The sensor can be placed in body areas that are rich in blood andwithout many other obstructions (such as bones). In the embodiments, thelocations are the earlobe, the hand (between the thumb and the indexfinger), between toes, on the lips, although other locations could beused. The sensor can be held in place temporarily by hand or attachedcontinuously.

Sensor for Food Stuff

In other embodiments, the device in accordance with the presentdisclosure is used to probe the properties of food stuff. That is, inembodiments, the biological material is food stuff. In otherembodiments, the biological material is packaged food stuff and thedevice in accordance with the present disclosure is arranged and/or usedto minimise reflection off the packaging. In embodiments, there istherefore provided an antireflection coating for packaging of foodstuff. In embodiments, the food stuff is oil such as olive oil orcomposite oils containing olive oil.

System Overview

In an embodiment, there is provided a sensor system comprising a sensor1303 that measures transmission through a sample under test (SUT), asoftware application (mobile, tablet, computer, etc.) that wirelesslyreceives the data in real time or whenever the connection becomesavailable, an online storage 1301 and database, and a clientapplication/interface that displays the data to a user or third party.This is shown in FIG. 13 .

The sensor comprises a transmitter and a receiver. In embodiments, thetransmitter comprises of one, two, or more antennas for generating theradiation, and the metamaterial (typically placed between the antennaand the sample) to enhance the penetration through the sample.

There is therefore provided a sensor comprising: a transmittercomprising a first antenna and a first device (for couplingelectromagnetic radiation, as described above) arranged to coupleelectromagnetic radiation emitted by the first antenna to a biologicalmaterial; and a receiver comprising a second antenna and a second device(for coupling electromagnetic radiation, as described above) arrange tocouple electromagnetic radiation transmitted by the biological materialto the second antenna.

A block diagram of the components in a sensor in accordance withembodiments is shown in FIG. 14 a . Some or all of the followingcomponents may be included: a battery 1407 for providing power; a screen1408 to display the data; and LEDs 1409 to provide visual feedback; avibration system 1411 to also provide feedback to the user; anelectronic calliper component 1410 that can measure the distancesbetween antennas; a printed circuit board 1401 that hosts theelectronics; a Bluetooth or other communications component 1402 totransmit information to a receiver; an impedance analyzer 1403 todirectly estimate the impedance of the sample under test; anaccelerometer 1404 to sense motion; an antenna system 1405 to generatethe radio wave signals; and the metamaterial component 1406 thatenhances the penetration of the radiation inside the sample under test.FIG. 14 b shows the components of a sensor in accordance with otherembodiments including an additional beam shaping element 1450. Inembodiments disclosed herein, the beam shaping element is a phasecorrector by way of example only.

In an embodiment, the transmitter further comprises a detector arrangedto detect electromagnetic radiation reflected by the biologicalmaterial. Advantageously, this allows for more accurate measurements ofthe biological material to be made.

In a further embodiment, the sensor is further arranged to determine thedistance between the transmitter and receiver. In another embodiment,the sensor is further arranged to determine the impedance of thebiological material. Advantageously, this allows the device to work withdifferent biological materials such as with different people. In anembodiment, the sensor further comprises an accelerometer.

The antenna, the metamaterial, or both, could be active, tunablecomponent so as to adjust their operation depending on theelectromagnetic properties (permittivity, permeability, impedance) ofthe sample under test. For example, when a different sample is testedthat has a slightly different impedance than the sample before it, theimpedance analyser will sense that, and the antenna & metamaterial willbe accordingly tuned to maximize the penetration through the sample.This can be achieved by integrating tunable electrical components suchas variable capacitors (varactors), inductors, or resistors.

That is, in an embodiment, the sensor further comprises variableresistors and/or capacitors coupled to an antenna and/or metamaterial toprovide tunability.

The sample under test may or may not be placed inside an enclosure orcontainer. The skin can be considered as a container for animal or humantissue. In an embodiment, the biological material is human or animaltissue. In an embodiment, the sensor is wearable. In a furtherembodiment, the sensor is arranged to be worn on a hand, a foot, an ear,or a lip or wherein the sensor is handheld.

In an embodiment, the biological material is food stuff. In anembodiment, the food stuff comprises at least one selected from thegroup comprising oil, milk, wine, coffee, and fruit juice and/or thefood stuff is bound by a container, optionally, a bottle or carton. Inan embodiment, the container comprises glass and/or plastic.

There is also provided a system comprising the sensor and furthercomprising: a wireless receiver arranged to receive data related to thebiological material from the sensor; a software application operating ona device remote to the sensor, the software application arranged toprocess the data; and an interface arranged to display the data and/orinformation related to the data. Advantageously, it may therefore bepossible to remotely monitor a sample. For example, a medicalprofessional may be able to remotely measure the blood sugar level of apatient.

FIGS. 15 a to 15 d show some examples of samples under test 1501, 1504,1505, 1506 with single and dual antenna 1503 and metamaterial 1502arrangements. FIG. 16 shows a tuning antenna 1602 including an impedanceanalyser 1603, metasurface 1601 for probing a sample under test 1604.

FIGS. 17 a to 17 c and 18 illustrate an example device in operation.

FIG. 18 a shows a sensor comprising two antenna 180 and two metasurfaces1802 arranged to improve coupling of electromagnetic radiation into andout of a human hand 1803. FIG. 18 b shows the sensor with additionalphase corrector components 1805.

FIG. 19 shows exploded views of metasurface with antenna configurationin periodic pattern (Top) and non-periodic pattern (Bottom).

FIG. 20 shows a layered device in accordance with embodiments comprisingthree metasurface layers 2001-2003 and an antenna layer 2004.

Advantageously, the device in accordance with embodiments of the presentdisclosure is passive. That is, it does not require a power supply. Thedevice may therefore increase the overall energy efficiency.

There is provided an antireflective medium for a glucose sensor, theantireflective medium comprising a metasurface. There is also providedan antireflective coating for a food stuff container, the antireflectivecoating comprising a metasurface.

Although aspects and embodiments have been described above, variationscan be made without departing from the inventive concepts disclosedherein.

EXAMPLE EXPERIMENTAL RESULTS

The two examples presented are glucose sensing in calibrated water-basedsamples, and oil sensing in oil mixtures. The measurements wereperformed in the 50-75 GHz band. The quantities presented are retrievedfrom the raw transmission and reflection recorded signals after applyingnoise filtering and other signal processing algorithmic operations.

Example 1: Glucose Sensing

FIG. 21 shows the correlation between the glucose concentration and theprocessed signal, repeated in two independently prepared samplesolutions around 60 GHz. The results indicate the repeatability of themethod and the algorithm utilized.

FIG. 22 compares the measurements obtained for three different types ofsample: samples consisting of water and varying amounts of glucose,sample consisting of water, salt (NaCl) and varying amounts of glucoseand samples consisting of water, varying amounts of salt and glucose.The results demonstrate that the three different solutions and theircorresponding concentrations can be completely distinguished from eachother. The purpose of using salt is that is a more realisticrepresentation of human blood.

FIG. 23 presents the processed signal as a function of glucoseconcentration for very low concentrations (the normal range for adultsis between 4 and 8 mMol/L) at a frequency of 68 GHz. It demonstratesthat very low glucose concentrations can be quantified.

Example 2: Oil Sensing

In this example the unknown concentration of palm kernel oil in amixture of palm kernel oil and rapeseed oil was determined for twodifferent experimental runs. The processed data are fitted with a linearequation, which can be used to exactly determine the concentration ofeach oil species in the mixture.

FIG. 24 shows output signal as a function of the concentration of palmkernel oil in a mixture of palm kernel and rapeseed oil.

FIG. 25 shows the processed signals from the radio wave reflectionmeasurements are fitted with an analytic Cole-Cole model, estimating therelaxation frequency of the model. Each oil species exhibits acharacteristic relaxation frequency, which can be used to identify anunknown oil species in a sample. In this case a single sensor is usedagainst the sample.

The sensor in accordance with embodiments is therefore highly effectiveat determining the concentration of oils in a mixture of oils.

What is claimed is:
 1. A sensor measurement device comprising: Animpedance analyzer to determine an impedance of a sample; a firstantenna configured to generate electromagnetic radiation having a firstwavelength; an impedance-matching device, positioned in a radiation pathbetween the first antenna and the sample, to receive the electromagneticradiation from the first antenna and transmit electromagnetic radiationof the first wavelength into the sample, the impedance-matching devicecomprising a metasurface including: a substrate having a thickness nogreater than the first wavelength of the electromagnetic radiation; anda plurality of elements supported by the substrate, wherein: theplurality of elements are spaced apart from one another across thesubstrate, each element has a first dimension no greater than the firstwavelength of the electromagnetic radiation, and at least two elementsof the plurality of elements differ in one or more of shape or size; anda second antenna configured to receive the electromagnetic radiationfrom the sample, wherein one or both of the first antenna and theimpedance-matching device are tunable based on the impedance of thesample to reduce an impedance mismatch along the radiation path.
 2. Thesensor measurement device of claim 1, wherein the sample comprises abiological sample.
 3. The sensor measurement device of claim 1, whereinthe metasurface is configured to impose a specific phase and amplitudechange along an incident wave of the electromagnetic radiation.
 4. Thesensor measurement device of claim 1, wherein, in the impedance-matchingdevice, the first dimension is the direction for propagation of theelectromagnetic radiation.
 5. The sensor measurement device of claim 1,wherein, in the impedance-matching device, at least one of the pluralityof elements has an irregular shape.
 6. The sensor measurement device ofclaim 1, wherein the sample is bound by a container, and wherein theimpedance-matching device is configured to transmit the electromagneticradiation of the first wavelength into the sample from a positionoutside the container.
 7. The sensor measurement device of claim 1,wherein, in the impedance-matching device, at least a subset of theplurality of elements are arranged in an irregular array.
 8. The sensormeasurement device of claim 1, wherein, in the impedance-matchingdevice, the plurality of elements are arranged in an irregular array. 9.The sensor measurement device of claim 1, wherein, in theimpedance-matching device, the substrate is a dielectric and theplurality of elements are conductive.
 10. The sensor measurement deviceof claim 1, wherein, in the impedance-matching device, the substrate isconductive and the plurality of elements are a dielectric.
 11. Thesensor measurement device of claim 1, wherein, in the impedance-matchingdevice, the plurality of elements are collectively arranged to resonateat the first wavelength of the electromagnetic radiation.
 12. The sensormeasurement device of claim 11, wherein the impedance-matching devicefurther comprises an additional metasurface coupled to the metasurface,wherein the additional metasurface comprises: a substrate comprising athickness no greater than a second wavelength of the electromagneticradiation; and a plurality of elements supported by the substrate,wherein: each element has a first dimension no greater than a secondwavelength of the electromagnetic radiation; at least two elements ofthe plurality of elements are non-identical; the additional metasurfaceis arranged, in cooperation with the metasurface, to resonate at asecond wavelength of the electromagnetic radiation; and the firstwavelength is different from the second wavelength.
 13. The sensormeasurement device of claim 12, wherein the additional metasurfaceshapes at least one of an amplitude or phase of the electromagneticradiation.
 14. The sensor measurement device of claim 1, furthercomprising an electronic calliper arranged to determine a distancebetween the first antenna and the second antenna.
 15. The sensormeasurement device of claim 1, wherein one or both of the first antennaand the impedance-matching device comprise a tunable component includingone or more of a varactor or a variable resister.
 16. The sensormeasurement device of claim 1, wherein: the sample comprises blood; thesensor measurement device is arranged to measure a blood glucose level;and the sensor measurement device is wearable on at least one of a hand,a foot, an ear, or a lip.
 17. The sensor measurement device of claim 1,wherein the first antenna, the impedance-matching device, and the secondantenna are physically associated.
 18. The sensor measurement device ofclaim 1, further comprising a second impedance-matching device arrangedbetween the sample and the second antenna to transmit electromagneticradiation of the first wavelength from the sample to the second antenna,the second impedance-matching device comprising a metasurface including:a substrate having a thickness no greater than the first wavelength; anda plurality of elements supported by the substrate, wherein: theplurality of elements are spaced apart from one another across thesubstrate; each element has a first dimension no greater than the firstwavelength, and at least two elements of the plurality of elementsdiffer in one or more of shape or size.
 19. A method of couplingelectromagnetic radiation into a sample using a sensor measurementdevice, the sensor measurement device comprising: an impedance analyzerto determine an impedance of a sample; a first antenna configured togenerate electromagnetic radiation having a first wavelength; animpedance-matching device, positioned in a radiation path between thefirst antenna and the sample, to receive the electromagnetic radiationfrom the first antenna and transmit electromagnetic radiation of thefirst wavelength into the sample, the impedance-matching devicecomprising a metasurface including: a substrate having a thickness nogreater than the first wavelength of the electromagnetic radiation; anda plurality of elements supported by the substrate, wherein: theplurality of elements are spaced apart from one another across thesubstrate, each element has a first dimension no greater than the firstwavelength of the electromagnetic radiation, and at least two elementsof the plurality of elements differ in one or more of shape or size; anda second antenna configured to receive electromagnetic radiation fromthe sample; the method comprising: positioning the sensor measurementdevice with respect to the sample such that the first antenna isdisposed on a first side of the sample and the second antenna isdisposed on a second side of the sample; determine an impedance of asample; tuning one or both of the first antenna or theimpedance-matching device based on the determined impedance to reduce animpedance mismatch along the radiation path; providing electromagneticradiation having the first wavelength from the first antenna to theimpedance-matching device; transmitting, by the impedance-matchingdevice, electromagnetic radiation having the first wavelength from thefirst antenna into the sample; receiving, by the second antenna,electromagnetic radiation from the sample; and characterizing the samplebased on the received electromagnetic radiation.
 20. A method fordesigning an impedance-matching device for a sensor measurement device,the sensor measurement device comprising: a first antenna configured togenerate electromagnetic radiation having a first wavelength; theimpedance-matching device, positioned in a radiation path between thefirst antenna and a test sample, to receive the electromagneticradiation from the first antenna and transmit the electromagneticradiation into the test sample, the impedance-matching device comprisinga metasurface including: a substrate having a thickness no greater thanthe first wavelength of the electromagnetic radiation; and a pluralityof elements supported by the substrate, wherein: the plurality ofelements are spaced apart from one another across the substrate, eachelement has a first dimension no greater than the first wavelength ofthe electromagnetic radiation, and at least two elements of theplurality of elements differ in one or more of shape or size; and asecond antenna configured to receive electromagnetic radiation from thesample; the method comprising: positioning the first antenna on a firstside of the test sample and the second antenna on a second side of thetest sample; determining an impedance of the test sample; calculating asheet impedance for the metasurface that will couple the electromagneticradiation of the first wavelength into the sample with maximumtransmission; and using analytical modelling to design the plurality ofelements of the metasurface such that, when the plurality of elementsare combined together in a pattern, cause the metasurface to have thecalculated sheet impedance.